Breeze taskbar: put less emphasis on the normal and minimized states

I find that the 'normal' and 'minimized' states for the Breeze taskbar get a little too much attention with their grey backgrounds.
This also has the side effect that the background of the panel is not continuous and changes a lot.
The proposed solution here is to remove these backgrounds, and use top bars instead.
The top bar is dark grey for the 'normal' state, and light grey for the 'minimized' state.

BEFORE:

AFTER:

Comments are welcome.